Lubricating oil composition for internal combustion engine

ABSTRACT

The invention provides a lubricating oil composition for internal combustion engines, containing a base oil composition containing a GTL base oil as a main component, and having % Cn of 14 to 25% and an aniline point of 120 to 126° C., and a comb-like polymethacrylate based viscosity index improver having a weight average molecular weight (Mw) of 400,000 or more, wherein a N sulfur content is 0.3 mass % or less based on a total weight of the lubricating oil composition.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for internal combustion engines. Specifically, the present invention relates to a lubricating oil composition for automobile engines (especially diesel engines). More specifically, the present invention relates to a lubricating oil composition for the internal combustion engines that is excellent in fuel efficiency, oil consumption control and detergency.

BACKGROUND OF THE INVENTION

A problem with crankcase lubricating oil is that the lubricating oil is liable to escape from the crankcase due to so-called blow-by gas. The blow-by gas or such a gas/lubricating oil mixture is preferably recycled to the engine rather than being discharged to the atmosphere. In some engines, such recycling is carried out by injecting the blow-by gas into an air intake system of the engine so that the lubricating oil burns in piston chambers. Recycling of blow-by gas solves the problem of emissions, whereas it may cause problems such as formation of deposits in the air intake system. For example, when the deposits form in an air compressor, the compressor does not work well and is further susceptible to damage. Also, for example, when there is an air cooler between the compressor and a cylinder block-crankcase, the air cooler may also be contaminated. It has been desired to provide a diesel engine system for preventing or further reducing the formation of such deposits as set out in JP5501620.

Meanwhile, low fuel consumption is required. To achieve low fuel consumption, studies have been carried out to prepare compositions having appropriate viscosity characteristics by using friction modifiers to contribute to friction reducing performance, and by using viscosity index improvers to reduce agitation resistance and to maintain an oil film at high temperatures while having a low viscosity at low temperatures, see JP2014210844.

However, there has been no lubricating oil composition that is satisfactory enough in suppressing formation of the deposits, and exhibiting fuel economy, and further maintaining such performance for a long time. Further, it is assumed that in future downsizing of commercial vehicles equipped with diesel engines and high supercharging will keep on advancing, and that thermal load on engine oil will also increase. However, there has been a problem that excellent volatility is not achieved in the conventional lubricating oil compositions.

As a result of intensive research by the present inventors, it has been found that the above-described problem can be solved by blending a GTL base oil and a comb-like polymethacrylate viscosity index improver, and this application has already been filed (JP2017119787).

An object of the present invention is to provide a lubricating oil composition for internal combustion engines for further improving the invention according to JP2017119787, the lubricating oil composition having a higher viscosity index and oil film retentivity so as to cope with advancing downsizing and high supercharging, and being excellent in detergency at high temperatures.

SUMMARY OF THE INVENTION

As a result of intensive research by the present inventors, it has been found that it is possible to solve aforementioned problems by preparing a specified base oil composition in the composition containing a GTL base oil and a comb-like polymethacrylate viscosity index improver. The present invention has been accomplished based on these findings.

That is, the present invention relates to a lubricating oil composition for internal combustion engines, comprising:

-   -   a base oil composition containing a GTL base oil as a main         component, and having % Cn of 14 to 25% and an aniline point of         120 to 126° C.; and     -   a comb-like polymethacrylate based viscosity index improver         having a weight average molecular weight (Mw) of 400,000 or         more,         wherein a sulfur content of the lubricating oil composition is         0.3 mass % or less based on a total weight of the lubricating         oil composition.

A kinematic viscosity at 100° C. of the base oil composition may be 3.5 to 8 mm2/s.

The lubricating oil composition may have SAE viscosity grade of 0W-20 or 5W-20 and a viscosity index of 180 or more, or the SAE viscosity grade of 5W-30 and the viscosity index of 220 or more.

A viscosity index of the base oil composition may be 120 or more.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, it is possible to provide a lubricating oil composition for internal combustion engines (especially automobile engines) having excellent oil film retentivity, engine detergency and fuel economy.

Hereinafter, the constituents (constituent elements), composition (content of constituent) and properties of the lubricating oil composition for internal combustion engines of the present invention will be described in detail, but the present invention is in no way limited by these.

The lubricating oil composition of the present invention contains a base oil composition containing a GTL base oil, a comb-like PMA based viscosity index improver, and other constituents if necessary.

In the present invention, the base oil composition containing only GTL base oil or a mixed base oil composition containing GTL base oil as a main component is used as the base oil.

Here, “the base oil composition containing a GTL base oil as a main component” means that the content of GTL base oil is 50 mass % or more, 60 mass % or more, 70 mass % or more, 80 mass % or more, or 90 mass % or more based on the total amount of the base oil composition. The upper limit value is not particularly limited and is 100 mass % or less.

The kinematic viscosity at 100° C. of the base oil composition according to the present invention is not particularly limited and preferably is 3.5 to 8.0 mm2/s, more preferably 3.5 mm²/s or more, 4.0 mm²/s or more, 4.5 mm²/s or more, 5.0 mm²/s or more, 5.5 mm²/s or more, 6.0 mm²/s or more, or 6.5 mm²/s or more. On the other hand, preferably 8.0 mm²/s or less, 7.5 mm²/s or less, 7.0 mm²/s or less or 6.5 mm²/s or less. By setting the kinematic viscosity at 100° C. of the base oil composition to the lower limit or more, satisfactory oil film retentivity can be obtained. Also, by setting the kinematic viscosity at 100° C. of the base oil composition to the upper limit or less, satisfactory fuel economy can be obtained.

Note that, in the present invention, the kinematic viscosity at 40° C., the kinematic viscosity at 100° C. and the viscosity index are measured in accordance with JIS K 2283-1993, respectively.

The % Cn of the base oil composition according to the present invention is 14 to 25, more preferably 14 or more, 15 or more or 16 or more, and preferably 25 or less, 24 or less, 23 or less, 22 or less or 21 or less. By setting the % Cn of the base oil composition within the above range, it is possible to obtain a lubricating oil composition having satisfactory viscosity index and oil film retentivity and seal compatibility by blending a comb-like PMA. If the % Cn of the base oil composition is less than the lower limit value, satisfactory viscosity index is not obtained and the viscosity of the lubricating oil composition under high pressure may be unfavorably excessively low. On the other hand, if the % Cn of the base oil composition exceeds the upper limit value, satisfactory viscosity index is not obtained and the sealing compatibility of the lubricating oil composition may be unfavorably deteriorated.

The % Ca of the base oil composition according to the present invention is not particularly limited. However, from the viewpoint of oxidative stability, it is preferably 10 or less, 5 or less, 3 or less, 2 or less, 1 or less, 0.5 or less, 0.3 or less, 0.1 or less or substantially 0.

Note that, “substantially 0” in the present invention means not only strictly zero but also containing only trace amounts below the measurement limit.

The % Cp of the base oil composition according to the present invention is not particularly limited, and it is the balance of % Cn and % Ca described above. Specifically, % Cp is 86 or less, 85 or less, or 80 or less and 65 or more, 70 or more, or 75 or more.

In the present invention, % Cn, % Ca and % Cp, respectively, represent the percentage of naphthene carbon number to the total carbon number, the percentage of aromatic carbon number to the total carbon number and the percentage of paraffin carbon number to the total carbon number, determined by a method (n-d-M ring analysis) in accordance with ASTM D 3238-85,

The aniline point of the base oil composition according to the present invention is 120 to 126° C. The aniline point in the present invention is measured by a method in accordance with ASTM D611 and JIS K2256.

The viscosity index of the base oil composition according to the present invention is not particularly limited. However, it is preferable to have a high viscosity index because of the social demands for low viscosity at low temperature for fuel saving. Therefore, the viscosity index of the base oil composition is preferably 110 or more, 115 or more, 120 or more, or 125 or more. The upper limit is not particularly limited, but it is usually 200 or less.

The sulfur content of the base oil composition according to the present invention is not particularly limited. However, if the sulfur content of the base oil composition is too high, high temperature detergency, oxidative stability and thermal stability of the lubricating oil composition may be adversely affected. Therefore, the sulfur content is preferably 1 mass % or less, 0.5 mass % or less, 0.3 mass % or less, 0.2 mass % or less, 0.1 mass % or less, or substantially 0 mass % based on the total weight of the base oil composition. Note that, “substantially 0 mass %” in the present invention means not only strictly zero but also containing only trace amounts below the measurement limit.

GTL (gas to liquid) oil synthesized by the Fischer-Tropsch process in the technology for liquefying fuels from natural gas used as a main component for the base oil of the lubricating oil composition according to the present invention. Using such base oils as main component makes it possible, in the framework of the present invention, to improve oxidative stability as well as reducing evaporative losses.

When using comb-like polymers, in comparison with mineral base oils (particularly Group III base oil derived from mineral oil), it is possible to improve fuel consumption by using GTL base oils because the temporary shear viscosity at 100° C. decreases especially within the framework of the present invention.

In the present invention, the kinematic viscosity at 100° C. of the GTL base oil is not particularly limited. Typically it is between 3.5 and 8.0 mm²/s. If the kinematic viscosity at 100° C. of the main component GTL base oil falls within this range, there is an advantage that the kinematic viscosity at 100° C. of the base oil composition can be easily adjusted within the aforementioned range.

Here, in order to obtain a GTL base oil having a kinematic viscosity at 100° C. of 3.5 to 8.0 mm²/s, a single GTL base oil having a kinematic viscosity at 100° C. of 3.5 to 8.0 mm²/s may be used. Or two or more kinds of GTL base oils may be mixed and prepared so that the kinematic viscosity at 100° C. falls within this range. When preparing from two or more kinds of GTL base oils, two kinds are preferably mixed, i.e. a GTL base oil (a1) having a kinematic viscosity at 100° C. of 2.5 to 6.0 mm²/s and a GTL base oil (a2) having a kinematic viscosity at 100° C. of 7.0 to 13 mm²/s). If the kinematic viscosity of the low viscosity base oil constituent (a1) at 100° C. is less than 2.5 mm²/s, the amount of evaporation increases, and it becomes difficult to maintain the viscosity of the composition over long periods. If using a high viscosity base oil constituent (a2) where the kinematic viscosity at 100° C. exceeds 13 mm²/s, the low temperature viscosity at −40° C. increases and startability at low temperature deteriorates. Furthermore, in this case, the viscosity index of the mixed GTL base oil is preferably from 120 to 180, more preferably from 120 to 150.

For these GTL base oils, the total sulfur content is preferably less than 10 ppm by mass, and the total nitrogen content is more preferably less than 1 ppm by mass. An example of such a GTL base oil product is Shell XHVI (registered trademark).

As long as the above properties are satisfied, the base oil composition according to the present invention may contain a base oil other than the GTL base oil. Or, the composition may be adjusted by blending other base oils so as to satisfy the above properties. As other base oils, either mineral oils or synthetic oils may be used, and any of Groups I to V, which are the base oil classification defined by API, may be used. Mixtures of these may also be used.

In the present invention, the base oil composition preferably contains the base oil belonging to Group II. The base oil of the group II is a mineral base oil having a saturated hydrocarbon (ASTM D 2007) of 90 vol. % or more, a sulfur content (ASTM D 1552) of 0.03 mass % or less, and a viscosity index (ASTM D 2270) of 80 to 120.

Group II base oil has low unsaturated carbon content and sulfur content, has sufficient oxidative stability and detergency, and has a certain % Cn. By blending the Group II base oil, % Cn of the base oil composition can easily be adjusted within the above range without impairing the properties of the lubricating oil composition.

That is, in the present invention, it is preferable to use a base oil composition containing or made up of a GTL base oil and a base oil belonging to Group II of API classification and satisfying the above-mentioned properties. In other words, it is preferable to use the base oil composition obtained by blending (in particular, a Group II base oil having % Cn not less than the above-mentioned lower limit value is blended in a GTL base oil having % Cn less than the lower limit value so that the % Cn of the base oil composition falls within the above range) the Group II base oil with the GTL base oil so that the % Cn of the base oil composition falls within the above range.

When the base oil composition contains a GTL base oil and a Group II base oil, the content of the Group II base oil is not particularly limited as long as the base oil composition satisfies the above properties. Typically, it is 1 mass % or more, 3 mass % or more, 5 mass % or more or 10 mass % or more, and 50 mass % or less, 45 mass % or less, 40 mass % or less, 35 mass % or less, 30 mass % or less, 25 mass % or less or 20 mass % or less.

The lubricating oil composition of the present invention includes a comb-like polymethacrylate based viscosity index improver (hereinafter also referred to as a comb PMA). The comb-like polymer represents a polymer having a plurality of extended side chains in a comb form relative to the main polymer chain. The viscosity index improvers of the present invention include, among these comb-like polymers, viscosity index improvers which are comb-like polymethacrylate-based polymers.

In the present invention, the “viscosity index improver” means a polymer having a weight average molecular weight (Mw) of not less than 50,000.

The weight average molecular weight (Mw) is obtained, for example, using Shodex GPC-101 high-performance liquid chromatography manufactured by Showa Denko K.K. More specifically, the weight-average molecular weight (weight average molecular weight in terms of polystyrene) can be analyzed (calculated) by using the range corresponding to the peak molecular weight, assuming that the temperature is 40° C., the detector is a differential refractive index detector (RI), the carrier flow rate is THF −1.0 ml/min (Ref 0.3 ml/min), the sample injection amount is 100 μl, and the column is {KF-G (Shodex)×1, KF-805 L (Shodex×2)}.

As a comb-like polymethacrylate based viscosity index improver according to the present invention, for example, a polymer described in JP-A-2010-532805 may be appropriately used. Also, its production method is not particularly limited.

The comb-like polymethacrylate based viscosity index improver according to the present invention preferably has a weight average molecular weight of 400,000 to 600,000, more preferably 400,000 to 500,000, and most preferably 400,000 to 450,000.

The PSSI (permanent shear stability index) of comb-like polymethacrylate based viscosity index improver according to the present invention is preferably 10 or less.

The PSSI of a polymer here in the present invention means a permanent shear stability index of the polymer calculated based on the data measured by ASTM D 6278-02 in accordance with ASTM D 6022-01.

Specific examples of such comb-like polymethacrylate based viscosity index improver include Viscoplex 3-201 (registered trademark), Viscoplex 3-220 (registered trademark), and the like.

The lubricating oil composition of the present invention may also include viscosity index improvers other than the comb-like polymethacrylate based viscosity index improvers. One example of such a viscosity index improver includes one or more polymers selected from the group consisting of non-comb-like PMA (polymethacrylates), OCP (olefin copolymers) and SCP (styrene-diene copolymers).

The non-comb-like PMA (polymethacrylates)-based viscosity index improver is not particularly limited and those known in art may be used. Those having a weight average molecular weight of 100,000 to 400,000 are preferred. Specific examples of such PMAs include those described in JP2014125569.

The OCP (olefin copolymers)-based viscosity index improver is not particularly limited and those known in art may be used. Those having a weight average molecular weight of 50,000 to 300,000 are preferred. Specific examples of such OCPs include those described in JP2014125569.

The SCP (styrene-diene copolymers)-based viscosity index improver is not particularly limited and those known in art may be used. Those having a weight average molecular weight of 200,000 to 1,000,000 are preferred. Specific examples of such SCPs include Infineum (registered trademark), SV 150, and the like.

Such viscosity index improvers (polymers having a weight average molecular weight of not less than 50,000) are generally blended in a diluted state in a suitable liquid medium to make them easier to handle. Also in the present invention, it may be blended in a diluted state in a liquid medium, and the amount of the liquid medium is sufficiently smaller than the base oil composition, so the effect of the liquid medium is neglectable. The liquid solvent is not particularly limited, but is typically a carrier oil which is a Group II base oil or a Group III base oil.

In the present invention, it has been found that the viscosity index of the lubricating oil composition is extremely improved by including the above comb-like PMA in the base oil composition containing a GTL base oil having % Cn within a predetermined range. Generally, the viscosity index of the base oil composition containing a lot of naphthenes (i.e., having a large % Cn) becomes relatively small. The present inventors also confirmed that the viscosity index of the base oil composition tends to decrease as the % Cn of the base oil composition increases.

However, surprisingly, the base oil composition having % Cn not less than the above lower limit has a lower viscosity index as compared to the base oil composition having % Cn less than the above lower limit value. In spite of this, when the same amount of comb-shaped PMA was blended therein, it was found that the viscosity index of the lubricating oil composition was larger for those derived from the former base oil composition. Thus, if the same amount of comb-like PMA is blended, fuel economy can be improved, or even if the blending amount of comb-like PMA is reduced, fuel economy and the like can be maintained. Reduction in the amount of comb-like PMA content also suppresses the sludge formation.

The lubricating oil composition of the present invention may contain constituents other than the above-mentioned depending on the purpose of use. Examples of the other constituents include detergents, dispersants, anti-wear agents, metal deactivators, antioxidants, defoaming agents and the like.

The lubricating oil composition of the present invention may contain a boron-containing detergent as a detergent. The boron-containing detergent includes, but is not particularly limited to, a boric acid-containing alkaline earth metal salt. More specifically, a borated alkaline earth metal alkyl salicylate detergent and a borated alkaline earth metal alkyl toluene sulfonate detergent may be mentioned. Borated calcium alkyl toluene sulfonate is particularly preferable.

Those known in the art may be used for such boron-containing detergents (for example, the borated alkaline earth metal alkyl toluene sulphonate detergents may be manufactured in accordance with the method described in JP-A-2008-297547).

Other detergents (boron-free detergents) other than the boron-containing detergent include, for example, metallic detergents. Examples of the metallic detergents include alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates, alkaline earth metal naphthenates and the like.

Examples of the alkaline earth metals include calcium and magnesium. These may be used singly or in combination of two or more. Usually, sulfonates, phenates, and salicylates of calcium or magnesium are preferably used.

Examples of the alkaline earth metal sulfonates include alkaline earth metal salts, especially magnesium salts, calcium salts and the like, of alkyl aromatic sulfonic acids having a straight chain or branched alkyl groups of carbon number 1 to 30, preferably 6 to 18. The production method thereof is arbitrary, for example, it may be obtained by sulfonating the alkyl aromatic compound having an alkyl group.

Examples of the alkaline earth metal phenates include alkaline earth metal salts, especially calcium salts, of alkylphenols, alkylphenol sulphides and alkylphenol Mannich reaction products having straight chain or branched alkyl groups of carbon number 4 to 30, preferably 6 to 18.

Examples of the alkaline earth metal salicylates include alkaline earth metal salts, particularly preferably magnesium salts and/or calcium salts, of alkyl salicylic acids having a straight chain or branched alkyl groups of carbon number 1 to 30, preferably 6 to 18.

The base numbers of these may be freely chosen according to the type and purpose of the corresponding lubricating oil.

The lubricating oil composition of the present invention may contain an ashless dispersant or a boron-containing dispersant as a dispersant. The ashless dispersant or the boron-containing dispersant is, for example, a polybutenyl succinimide based, a polybutenyl succinamide based, a benzylamine based, a succinate ester based dispersant or the like, or a borated product thereof.

Polybutenyl succinimides are obtained from polybutenes obtained by polymerisation of high-purity isobutene or mixtures of 1-butene and isobutene using a fluorinated boron based catalyst or an aluminium chloride based catalyst, and the products having a vinylidene structure at the polybutene terminals are normally contained in the amount of 5 to 100 mol %. From the viewpoint of obtaining sludge inhibiting effects, it is preferable to include 2 to 5, and in particular 3 to 4, nitrogen atoms in the polyalkylene polyamine chains. Further, examples of the polybutenyl succinimide derivatives that can be used include so-called modified succinimides in which some or all of the amino and/or imino groups present have been neutralised or amidified by making boric acid compounds such as boric acid or oxygen-containing organic compounds such as alcohols, aldehydes, ketones, alkylphenols, cyclic carbonates and organic acids act on the aforementioned polybutenyl succinimides.

Examples of anti-wear agents imparting wear resistance and extreme pressure property that can be used in the lubricating oil composition of the present invention include zinc dithiophosphates (ZnDTP). Examples of ZnDTP generally include zinc dialkyldithiophosphates, zinc diaryldithiophosphates and zinc arylalkyldithiophosphates.

The alkyl groups here may be straight-chain or branched. Examples of the alkyl groups of the zinc dialkyldithiophosphates that can be used include zinc dialkyldithiophosphates having primary or secondary alkyl groups of carbon number 3 to 22 or alkylaryl groups substituted with alkyl groups of carbon number 3 to 18 may be used.

Specific examples of zinc dialkyl dithiophosphates include of zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate, zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zinc diisopentyl dithiophosphate, zinc diethylhexyl dithiophosphate, zinc dioctyl dithiophosphate, zinc dinonyl dithiophosphate, zinc dodecyl dithiophosphate, zinc didodecyl dithiophosphate, zinc dipropylphenyl dithiophosphate, zinc dipentylphenyl dithiophosphate, zinc dipropylmethylphenyl dithiophosphate, zinc dinonylphenyl dithiophosphate, zinc didodecylphenyl dithiophosphate and zinc didodecylphenyl dithiophosphate.

The metal deactivators that can be used in the lubricating oil composition of the present invention include benzotriazoles and benzotriazole derivatives such as alkyl-tolyltriazoles, and benzimidazoles and benzimidazole derivatives such as tolimidazoles. Further examples include indazole derivatives such as tolylindazoles, benzothiazoles and benzothiazole derivatives such as tolylthiazoles. Examples also include benzoxazole derivatives, thiadiazole derivatives and triazole derivatives.

Examples of the antioxidants used in the lubricating oil composition of the present invention include amine-based antioxidants and phenol-based antioxidants.

Examples of amine-based antioxidants include dialkyl diphenylamines such as p, p′-dioctyl-diphenylamine (Nonflex OD-3 manufactured by Seiko Chemical Ltd.), ρ,ρ′-di-α-methylbenzyl diphenylamine and N-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and monooctyldiphenylamine, bis (dialkylphenyl) amines such as di (2,4-diethylphenyl) amine and di (2-ethyl-4-nonylphenyl) amine, alkylphenyl-1-naphthylamines such as octyl-phenyl-1-naphthylamine and N-t-dodecylphenyl-1-naphthylamine, aryl naphthylamines such as 1-naphthylamine, phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines such as N, N′-diisopropyl-p-phenylenediamine and N, N′-diphenyl-p-phenylenediamine, and phenothiazines such as Phenothiazine (manufactured by Hodogaya Chemical Ltd.) and 3, 7-dioctylphenothiazine.

Phenol-based antioxidants include 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2, 4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone (Antage DBH, manufactured by Kawaguchi Chemical Industry Co. Ltd.); 2, 6-di-t-butyl-4-alkylphenols such as 2, 6-di-t-butylphenol, 2, 6-di-t-butyl-4-methylphenol and 2, 6-di-t-butyl-4-ethylphenol; 2, 6-di-t-butyl-4-alkoxyphenols such as 2, 6-di-t-butyl-4-methoxyphenol and 2, 6-di-t-butyl-4-ethoxyphenol. Also, there are 3,5-di-t-butyl-4-hydroxybenzylmercapto-octylacetate, alkyl-3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionates such as n-octadecyl-3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate (Yoshinox SS, manufactured by Yoshitomi Pharmaceutical Industries Ltd.), n-dodecyl-3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate and 2′-ethylhexyl-3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate, and benzenepropanoic acid 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-C7˜C9 side-chain alkyl ester (Irganox L135, manufactured by Ciba Specialty Chemicals Ltd.); 2, 6-di-t-butyl-α-dimethylamino-p-cresol, and 2,2′-methylenebis (4-alkyl-6-t-butylphenol) such as 2,2′-methylenebis (4-methyl-6-t-butylphenol) (Antage W-400, manufactured by Kawaguchi Chemical Industry Ltd.) and 2,2′-methylenebis (4-ethyl-6-t-butylphenol) (Antage W-500, manufactured by Kawaguchi Chemical Industry Ltd.). Furthermore, there are bisphenols such as 4, 4′-butylidenebis (3-methyl-6-t-butylphenol) (Antage W-300, manufactured by Kawaguchi Chemical Industry Ltd.), 4, 4′-methylenebis (2, 6-di-t-butylphenol) (Ionox 220AH, manufactured by Shell Japan Ltd.), 4, 4′-bis (2, 6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl) propane (Bisphenol A, manufactured by Shell Japan Ltd.), 2, 2-bis (3, 5-di-t-butyl-4-hydroxyphenyl) propane, 4,4′-cyclohexylidenebis (2, 6-t-butylphenol), hexamethylene glycol bis [3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate] (Irganox L109, manufactured by Ciba Specialty Chemicals Ltd.), triethylene glycol bis [3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionate] (Tominox 917, manufactured by Yoshitomi Pharmaceutical Industries Ltd.), 2, 2′-thio-[diethyl-3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox L115, manufactured by Ciba Specialty Chemicals Ltd.), 3, 9-bis {1, 1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy]ethyl} 2,4,8, 10-tetraoxaspiro [5,5] undecane (Sumilizer GA80, manufactured by Sumitomo Chemicals), 4,4′-thiobis (3-methyl-6-t-butylphenol) (Antage RC, manufactured by Kawaguchi Chemical Industry Ltd.) and 2, 2′-thiobis (4, 6-di-t-butyl-resorcinol). There are also polyphenols such as tetrakis [methylene-3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate] methane (Irganox L101, manufactured by Ciba Specialty Chemicals Ltd.), 1, 1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane (Yoshinox 930, manufactured by Yoshitomi Pharmaceutical Industries Ltd.), 1, 3, 5-trimethyl-2, 4, 6-tris (3, 5-di-t-butyl-4-hydroxybenzyl) benzene (Ionox 330, manufactured by Shell Japan Ltd.), bis-[3, 3′-bis-(4′-hydroxy-3′-t-butylphenyl) butyric acid] glycol ester, 2-(3′, 5′-di-t-butyl-4-hydroxyphenyl) methyl-4-(2″, 4″-di-t-butyl-3″-hydroxyphenyl) methyl-6-t-butylphenol and 2, 6, -bis (2′-hydroxy-3′-t-butyl-5′-methyl-benzyl)-4-methylphenol, and phenol-aldehyde condensates such as condensates of p-t-butylphenol and formaldehyde and condensates of p-t-butylphenol and acetaldehyde.

Examples of the defoaming agent that can be used in the lubricating oil composition of the present invention include organosilicates such as dimethylpolysiloxane, diethylsilicate, fluorosilicone and the like, and non-silicone based defoaming agents such as polyalkyl acrylate.

The content of the base oil is preferably from 60 to 90 mass %, more preferably from 65 to 90 mass %, further preferably from 70 to 85 mass %, based on the total mass of the lubricating oil composition.

The content of the viscosity index improvers (total viscosity index improver content) is not particularly limited and may be modified as appropriate. For example, it may be 0.05 to 20 mass % and the like based on the total mass of the lubricating oil composition. The preferable amounts of each viscosity index improver are given below.

The content of the comb-like PMA is not particularly limited. It is preferably from 1.0 to 10 mass %, more preferably from 1.5 to 9.0 mass %, and further preferably from 2.0 to 8.0 mass %, based on the total mass of the lubricating oil composition. Particularly, when the SAE viscosity grade of the lubricating oil composition is 0W-20 or 5 W-20, the content thereof is preferably in the range of 2.0 to 7.0 mass %, 2.0 to 6.0 mass %, 2.0 to 5.0 mass %, and 3.0 to 4.0 mass %. On the other hand, when the SAE viscosity grade of the lubricating oil composition is 5W-30, the content thereof is preferably in the range of 3.0 to 8.0 mass %, 4.0 to 8.0 mass %, 5.0 to 8.0 mass %, and 6.0 to 8.0 mass %

The content of the non-comb-like PMA is not particularly limited, but the ratio of the non-comb-like PMA content to the total viscosity index improver content (non-comb-like PMA content/total viscosity index improver content) is preferably not more than 0.7.

The content of the OCP is not particularly limited, but the ratio of the OCP content to the total content index improver content (OCP content/total viscosity index improver content) is preferably not more than 0.2.

The content of the SCP is not particularly limited, but the ratio of the SCP content to the total content index improver content (SCP content/total viscosity index improver content) is preferably not more than 0.3.

If non-comb-like PMA (polymethacrylates), SCP styrene-diene copolymers) and/or OCP (olefin copolymers) are included as viscosity index improvers, and these satisfy at least one (but preferably all) of the aforementioned ranges, it is possible within the framework of this invention to achieve the effects of the invention and also to reduce manufacturing costs.

The contents of other constituents which may be preferably added to the lubricating oil composition of the present invention are described below.

The total amount of the boron-containing detergent and the boron-containing dispersant (total), singly or in combination, is preferably, for example, 0.025 mass % or more based on the total amount of the composition in terms of boron content (total value). Whereas, the upper limit value is, for example, 0.1 mass % or less and 0.050 mass % or less.

The content of the metallic detergent, singly or in combination, is preferably from 0.05 to 0.3 mass %, more preferably from 0.1 to 0.2 mass % in terms of the metal amount based on the total mass of the lubricating oil composition.

The content of the ashless dispersant, singly or in combination, is preferably such an amount as to provide, for example, 0.01 to 0.3 mass % of nitrogen based on the total mass of the lubricating oil composition.

The content of the anti-wear agent (for example, ZnDTP), singly or in combination, is preferably in the range of 0.01 to 0.10 mass %, more preferably 0.05 to 0.08 mass %, as the phosphorus (P) amount based on the total mass of the lubricating oil composition.

The content of the metal deactivator, singly or in combination, is preferably in the range of 0.01 to 0.5 mass % based on the total mass of the lubricating oil composition.

The content of the antioxidant, singly or in combination, is preferably in range of 0.01 to 2 mass % based on the total mass of the lubricating oil composition.

The content of the defoaming agent, singly or in combination, is preferably in the range of 0.0001 to 0.01 mass % based on the total mass of the lubricating oil composition.

The lubricating oil composition according to the present invention containing the above constituents in the above composition may be easily adjusted to satisfy or fulfil the following properties naturally.

The sulfur content of the lubricating oil composition is adjusted so as to be 0.3 mass % or less, 0.28 mass % or less, 0.26 mass % or less or 0.25 mass % or less based on the total weight of the lubricating oil composition from the viewpoints of high temperature detergency, oxidative stability and thermal stability.

The viscosity of the lubricating oil composition is not particularly limited. However, the composition is preferably adjusted such that the SAE viscosity grade conform is 0W-20 or 5W-20 or 5W-30. In order to correspond to the SAE viscosity grade, it is preferable to adjust the kinematic viscosity at 100° C. of the lubricating oil composition to not less than 5.6 mm²/s and less than 12.5 mm²/s.

The viscosity index of the lubricating oil composition is not particularly limited. However, it is preferable to have a high viscosity index because of the social demands for low viscosity at low temperature for fuel saving. Therefore, the viscosity index of the lubricating oil composition is preferably 180 or more. The upper limit is not particularly limited, but it is usually 300 or less. If the SAE viscosity grade is 5W-30, the viscosity index of the lubricating oil composition is preferably 220 or more.

Examples

The present invention will now be described in more detail with reference to Examples and Comparative Examples, but the present invention is in no way limited by these Examples.

The raw materials used in this example are as follows. Properties of each base oil are shown in Table 1.

Base Oils

Base oil-1: XHVI-4 RL (GTL oil) Base oil-2: XHVI-8RL (GTL Oil) Base oil-3: Kixx 150 N (Group II base oil) Base oil-4: Kixx 600 N (Group II base oil) Base oil-5: HVI 60 (Group I base oil) Base oil-6: HVI 160 S (Group I base oil)

Viscosity Index Improvers

Viscosity index improver solution: A solution containing a comb-like PMA based viscosity index improver having a weight average molecular weight of 400,000 (comb-like PMA concentration 60 mass %).

Other Additives

Defoaming agent solution: A solution containing dimethyl polysiloxane having a concentration of 3 mass %

Additive Package: Additive package equivalent to JASO DL-1 having sulfated ash content of 0.46 mass % when 11.7% was added

The base oils were blended at the mass ratio shown in the following Table 1 (adjusted so that the kinematic viscosity at 100° C. of the base oil composition was about 6.0 mm2/s) to obtain a base oil composition, and further various additives were blended to obtain the lubricating oil compositions according to Examples 1 to 4 and Comparative Examples 1 to 5. the kinematic viscosity at 100° C., viscosity index, % Cp, % Cn, % Ca, and the aniline point of each prepared base oil composition are shown in Table 1.

TABLE 1 Comp Comp Comp Comp Comp Ex-1 Ex-2 Ex-3 Ex-4 Ex-1 Ex-2 Ex-3 Ex-4 Ex-5 Base oil-1 54.32 61.72 20.56 57.20 37.00 60.05 34.31 Base oil-2 13.98 20.56 45.27 41.96 Base oil-3 41.15 74.04 Base oil-4 13.97 20.55 19.07 8.23 Base oil-5 65.81 Base oil-6 22.22 16.46 KV100. of base 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 oil (mm²/s) Base oil VI 126 123 121 123 135 120 104 106 135 Base oil % Cp 85.2 83.1 80.2 83.1 89.9 82.6 69.5 69.6 89.9 Base oil % Cn 14.8 16.9 19.8 16.9 10.1 16.5 27.5 30.4 10.1 Base oil % Ca 0.0 0.0 0.0 0.0 0.0 0.9 3.0 0.0 0.0 Base oil aniline 125.4 123.8 122.8 123.8 128.8 120.2 104.3 116.9 128.8 point (° C.) Viscosity index 6.00 6.00 6.00 12.00 6.00 6.00 6.00 6.00 12.00 improver (3.60) (3.60) (3.60) (7.20) (3.60) (3.60) (3.60) (3.60) (7.20) solution (comb-like PMA) Defoaming 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 agent solution Additive 11.70 11.70 11.70 11.70 11.70 11.70 11.70 11.70 11.70 package Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Next, the following evaluation tests were carried out for the lubricating oil compositions of Examples and Comparative Examples.

The oil film thickness was measured using an EHD 2 oil film thickness meter manufactured by PCS. The oil film thickness (nm) at a rotational speed of 20 mm/s was measured by rotating from a rotation speed of 3000 mm/s to 10 mm/s under an oil temperature of 120° C., a sliding ratio of 20% and a load of 20 N. The larger the numerical value, the thicker the oil film, and the better the lubricating property.

Detergency was evaluated by a panel coking test in accordance with FED No. 791 Rev. B Test Method 3462. The operation of splashing the lubricating oil composition continued for 3 hours by the rotating blade in a cycle of “rotating for 15 seconds at a speed of 1000 rpm and then stopping for 45 seconds”, at an oil temperature of 100° C. and an aluminum panel temperature of 300° C. After 3 hours, the mass (mg) of the deposit adhering to the aluminum panel was measured. The smaller the numerical value, the better the detergency.

The kinematic viscosity (KV40) at 40° C., the kinematic viscosity (KV100) at 100° C., the viscosity index (VI), the CCS viscosity at −30° C. (CCS-30° C.) of the lubricating oil composition of each Example and Comparative Example were measured. Also, the calcium, magnesium, zinc, phosphorus, molybdenum, boron, nitrogen, sulfur contents and the sulfated ash content were determined, and shown together with the results of the evaluation test described above in Table 2 below.

TABLE 2 Comp Comp Comp Comp Comp Ex-1 Ex-2 Ex-3 Ex-4 Ex-1 Ex-2 Ex-3 Ex-4 Ex-5 Viscosity 5W-20 5W-20 5W-20 5W-30 5W-20 5W-20 10W-30 10W-30 5W-30 grade KV40 (mm²/s) 43.94 42.94 47.89 47.00 46.64 43.48 58.96 52.21 50.33 KV100 8.756 8.680 9.297 11.00 8.996 8.898 10.79 9.804 10.88 (mm²/s) VI 183 186 181 236 178 191 177 177 215 CCS-30° C. 4300 4400 4500 4500 4100 4670 13600 8700 4300 mPa · s Ca (mass %) 0.093 0.093 0.093 0.093 0.093 0.093 0.093 0.093 0.093 Mg (mass %) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Zn (mass %) 0.091 0.091 0.091 0.091 0.091 0.091 0.091 0.091 0.091 P (mass %) 0.078 0.078 0.078 0.078 0.078 0.078 0.078 0.078 0.078 Mo (mass %) 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 B (mass %) 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 N (mass %) 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 S(mass %) 0.25 0.24 0.24 0.24 0.25 0.38 0.66 0.24 0.24 S-ash (mass %) 0.46 0.46 0.46 0.46 0.46 0.46 0.46 0.46 0.46 Oil film 5.5 5.9 5.2 5.8 2.9 5.6 5.9 5.7 3.1 thickness (nm) Panel coking 12.4 14.2 17.5 18.1 14.0 25.2 26.1 17.8 19.2 test (mg) Viscosity ∘ ∘ ∘ ∘ x ∘ x x x index Oil film ∘ ∘ ∘ ∘ x ∘ ∘ ∘ x thickness High ∘ ∘ ∘ ∘ ∘ x x ∘ ∘ temperature detergency (panel coking)

It is clear from Tables 1 and 2 that the compositions of Examples satisfying this specification satisfy all of the viscosity index, the oil film thickness, and the high temperature detergency, whereas the compositions of the Comparative Examples that do not satisfy this specification are inferior in either viscosity index, oil film thickness, or high temperature detergency. 

1. A lubricating oil composition for internal combustion engines, comprising: a base oil composition containing a GTL base oil as a main component, and having % Cn of 14 to 25% and aniline point of 120 to 126° C.; and a comb-like polymethacrylate based viscosity index improver having a weight average molecular weight (Mw) of 400,000 or more, wherein, a sulfur content is 0.3 mass % or less based on the total weight of the lubricating oil composition.
 2. The lubricating oil composition for internal combustion engines according to claim 1, wherein a kinematic viscosity at 100° C. of the base oil composition is 3.5 to 8 mm2/s.
 3. The lubricating oil composition for internal combustion engines according to claim 1, wherein an SAE viscosity grade is 0W-20 or 5W-20 and a viscosity index is 180 or more, or the SAE viscosity grade is 5W-30 and the viscosity index is 220 or more.
 4. The lubricating oil composition for internal combustion engines according to claim 1, wherein a viscosity index of the base oil composition is 120 or more.
 5. The lubricating oil composition for internal combustion engines according to claim 1, wherein the base oil composition contains a GTL base oil and a base oil belonging to Group II of API classification. 